The present study was conducted to investigate the antibiotic resistance of 24 Salmonella gallinarum isolated from 48 chicken samples of diagnosed fowl typhoid cases during the period from November 1998 to November 1999. And the isolates of S gallinarum were also tested for their invasion abilities to experimental infection as one of virulence tests, and the presence of virulence-related plasmid in S gallinarum isolates. The results obtained through this study were summarized as follows; 1. All of isolates from 48 cases of 24 farms were identified S gallinarum by biochemical and serological tests.2. Antimicrobial drug resistance test against 24 isolates showed that the isolates were resistant to Colistin(95.8%), and Penicillin(79.2%), Polymyxin B(75.0%), Streptomycin (65.2%), Gentamycin(54.2%), and Tetracycline(33.3%). 3. Mortality in chicken following peroral inoculation of four isolates of S gallinarum during 14-days inoculation pecked at 5 days(40%) after inoculation and all of experimental chickens died within 13 days after inoculation.4. Based on the pattern and number of isolated plasmid from each isolate, plasmid profiles were divided into five groups; group I with 3 plasmids, group II to group IV with 4 plasmids and group V with 5 plasmids.